The leaders of North Korea and China have marked the 75th anniversary of their diplomatic relations by exchanging messages that expressed hopes for stronger ties, as outsiders raised questions about their relationship.

The alliance between China and North Korea — and more broadly, Iran and Russia — is a growing security concern for the West.

China and North Korea marked the 75th anniversary of their diplomatic relations on Sunday with little fanfare and no publicly reported major events, in contrast to earlier pledges from both leaders to celebrate the milestone with displays of camaraderie in the designated "Year of Friendship.

The leaders of China and North Korea vowed on Sunday to enhance bilateral cooperation on the 75th anniversary of diplomatic relations between the two countries, Pyongyang's state news agency KCNA reported.

The leaders of North Korea and China marked the 75th anniversary of their diplomatic relations on Sunday by exchanging messages that expressed hopes for stronger ties, as outsiders raised questions about their relationship.

The top diplomats of North Korea and China have pledged to further develop relations between their countries as they exchanged messages to mark the 75th anniversary of diplomatic ties, the North's state media reported on Monday.

North Korean leader Kim Jong-un and Chinese President Xi Jinping hailed the 75th anniversary of their countries' establishment of diplomatic relations on Sunday by exchanging messages that expressed hope for stronger ties.